DNA polymerase k (pol k) is the major replicative DNA polymerase in higher eukaryotes. Proliferating cell nuclear antigen (PCNA) dramatically increases the processivity of pol k, by increasing its rate of incorporation of nucleotides and decreasing its dissociation from its template-primer. The simplest replication complex would contain pol k (composed of two subunits, of 125 kD and 50 kD), PCNA (likely a trimer), a DNA template and a DNA primer. The STEM is being used to characterize this complex. To aid in the orientation of the components, the template DNA was extended to a 35-mer with biotinylated dAMP residues to be labeled with Au1.4nm-streptavidin. The resulting pol k, PCNA, Au-streptavidin, 35-21-mer complex was observed and had the appropriate mass. Additional experiments are underway identify the components in this complex by using labeled antibodies.